Low oil pressure - sticking release valve?

[timo22]

A couple of weeks ago the low oil pressure light came on a couple of times after driving on the motorway for a while, I had it checked out and the filter had broken up a fair bit. It had been in for just under 10000 miles. An oil and filter change seemed to make it better, although now I'm getting similar issues. It's generally fine with driving about town, but when I come off a motorway I get warnings when setting off from stationary. Sometimes they clear with a quick throttle boost, if not I stop ASAP. If I turn the engine off and let it sit for a few minutes I can generally get another 20-30 mins driving out of it.

 

I took the sump off to see if there was any gunge in there or the pump pickup screen was blocked but to no avail. Could it be the pressure release valve getting stuck? It would seem to fit low pressure issues after travelling at higher revs when the valve may have been open more and got stuck. And if it got stuck shut might that explain the blown out filter? Not entirely sure how letting it sit for a few minutes would always let it clear if it had gunk in.

 

Any advice would be much appreciated!

[KenONeill]

It also fits with residue from the filter getting stuck in the pressure monitor valve, which is easier and cheaper to change.

[timo22]

Do you mean the pressure switch on the front of the engine? Forgot to say I changed that, although there could be more filter debris stuck in this one... If not, where is the monitor valve?

[KenONeill]

I meant the transducer that drives the oil pressure light. I've seen this give false LP readings due to debris in the capillary.

[Breezy_Pete]

I think the indications suggest a real, though possibly marginal issue with the oil pressure. It appears when the oil has got hottest/least viscous, but the radiator cooling, and rpm suddenly reduces (coming off motorway, transition to slow airflow/slow speed). Stopping the engine for a while is cooling everything enough to push you to the good side of marginal. I would recommend another, rather immediate, oil and filter change, as the replacement one following the failed one may be clogged with small debris from that.

My only hands-on experience of an oil pressure relief valve was on a different marque, but my impressions of it were "that's so robust and simple I can't see that causing trouble:" (And on that occasion it was a pick-up blockage).

[Breezy_Pete]

Also, as Ken says, worth checking that your new pressure switch hasn't got debris up its 'business end', nor oil seeping out anywhere, as that costs nothing but a little time.